How does Turbo work with Action Cable?

Modern Rails makes it easy to build real-time features into your app. With the turbo-rails library, you can add a call to turbo_stream_from in a view file, and that will set up a WebSocket connection between your app server and all browsers that render that view. Your application can then use the broadcast_* family of methods to send elements to all those browsers. Turbo, on receiving the elements, will add them to the DOM, which will trigger DOM updates. Users thus see updates from the server in real-time, without having had to make separate requests. The amazing thing is that the broadcast_* methods can be called from any process (e.g. asynchronous jobs, the Rails console etc), and not just the Rails server process. How does this magic work? What is a WebSocket connection and how is it different from HTTP? How do Turbo and ActionCable create a WebSocket connection? How do the broadcast_* methods work across processes? Are these connections secure?.